A common type of integrated circuit (IC) device is a metal-oxide-semiconductor field effect transistor (MOSFET). A MOSFET is a field-effect device that includes a source region, a drain region, a channel region extending between the source and drain regions, and a gate provided over the channel region. The gate includes a conductive gate structure disposed over the channel region. The conductive gate is typically insulated from the channel region by a thin oxide layer.
High-voltage, field-effect transistors (HVFETs) are also well known in the semiconductor arts. Many HVFETs employ a device structure that includes an extended drain region, also known as the drift region, that supports or “blocks” the applied high-voltage (e.g., 150 volts or more) when the device is in the “off” state. HVFETs in a high-voltage integrated circuit (HVIC) process are commonly formed as lateral device structures where source and drain are on the top surface of the semiconductor die. The channel and the drift regions separate the source from the drain. The gate over the channel region is used to switch the HVFET on or off and the drift region supports the drain voltage. The length of the drift region between the channel and the drain determines the maximum voltage that the device can support. Devices with different voltage capabilities can be integrated in the same HVIC process by modifying the drift length. In the context of the present application, a medium-voltage device refers to voltages in the range of 50V to 150V. A medium voltage FET can be integrated in the same HVIC process that has the HVFET that can support voltages higher than 150V.
The operating characteristics of a high voltage or power IC device is typically set or programmed by selectively opening (or closing) one or more electrical connections. A zener diode is one type of electrical element used to trim or program analog parameters (e.g., frequency) of a power IC device. A zener diode provides a normally off or non-conducting electrical connection. To change the conducting state of the zener element a high voltage (>10 V) is typically applied to breakdown the zener, with the large resulting current (150-200 mA) shorting the anode and cathode terminals of the zener permanently. The cumulative current flowing through the zener elements may be used to program one or more analog parameters. For example, based on the state of one or more zener elements, an analog parameter such as frequency may be set within a specified tolerance in the controller section of the power IC.